Stem cells, both embryonic and somatic, theoretically hold great promise for tissue regeneration and the restoration of organ function in human diseases. In particular, the purification and characterization of human neural stem cells (hNSCs) has shown potential for neural repair and the development of new hNSC-based transplantation strategies for the treatment of aspects of eurodegenerative disorders. However, a lack of understanding of the mechanisms by which the local microenvironment regulates the fate of hNSCs reflects a gap in our knowledge of fundamental stem cell biology and remains one of the obstacles to effective therapies. Extracellular matrix (ECM) contributes to the complex structure of the brain's neurogenic microenvironment. In addition to providing structure, hyaluronic acid (HA), a major component of the ECM, possesses a regulatory function via its interactions with CD44, its cell surface receptor, which is expressed by hNSCs. Micro array analysis suggests that high molecular weight HA significantly changes the expression of 24 genes, at least two. MFRP (membrane-type frizzled-related protein) and ICDAP-1alpha (integrin cytoplasmic domain-associated protein-1 alpha) can determine the behavioral choices of hNSCs. This K18 training grant application, sponsored by Dr. Evan Snyder, director of The Burnham Institute's Stem Cell Program, is designed to address the question of how the CD44/HA pathway regulates the fate of hNSCs. Based on our preliminary data, we hypothesize that HA contributes to the neurogenic regulatory network by interacting with CD44 expressed on hNSCs and initiating signal transduction pathways that subsequently result in differential gene expression and the reprogramming of hNSCs behavior. In Specific Aim #1, we will investigate the effect of HA on cytoskeleton organization and MAPK phosphorylation in hNSCs. In Specific Aim #2, we will examine the effect of HA on the expression of MFRP and ICDAP-1alpha and whether the effect of HA on the differential expression of MFRP and ICDAP-1alpha is mediated by CD44 in hNSCs. Overall, in addition to providing training opportunities, this proposal will allow us to test a novel hypothesis and to generate data for further studies on the role of the CD44/HA pathway in regulation of hNSCs fate.